MACON, Georgia (41NBC/WMGT) – An investigation found faulty work done at Robins Air Force Base is to blame for a deadly plane crash involving more than a dozen service members.

41NBC obtained copies of the investigation led by the Fourth Marine Aircraft Wing. The report says what caused the crash last July was a corroded propeller blade that broke.

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According to documents, a blade on the KC-130T had corrosion. While being overhauled at Robins Air Force Base in 2011, a protective coating was put over the corrosion, which is proof of damage that has been there since Robins was doing work on the plane. Documents say coating is part of the overhauling process, but the corrosion should have been fixed, or condemned.

As a result, a crack formed causing the blade to break off. The plane plummeted to the ground from 20,000 feet, killing 15 marines and a U.S. Navy Sailor.

The left side blade, closest to the engine, tore into the fuselage causing the plane to go down.

They were on their way to a naval air facility in El Centro, California. The plane crashed in a soybean field in Mississippi.

Representative Austin Scott, who works closely with Robins released this statement:

“The crash of Yanky 72 is a horrible tragedy that killed fifteen Marines and a Sailor. It is a reminder of the risk that our men and women in the military take every day…I am confident that Air Force leadership is addressing this from a process level, and I will continue to engage on this and other readiness issues facing our forces.”

Robins Air Force released answers to questions 41NBC sent via email:

Q1. What exactly happened on Robins’ end and how have mistakes been fixed to prevent this in the future?
A1. Corrosion that was present at the time of overhaul should have been detectable utilizing the inspection procedures that were in place at the time of the overhaul. The intergranular crack which grew, and eventually led to a fatigue crack which caused the blade to fail, may not have been detectable utilizing the inspection procedures that were in place at the time of the overhaul. It is unknown why the blade completed its overhaul with the corrosion and crack still present.

Although this propeller separation event is an extremely rare occurrence, this incident exposed the risk to us. As is the case here, corrosion naturally occurs. The presence of blades coming to the depot with corrosion is not at all unusual. Corrosion can lead to intergranular cracking, but it is not the only cause. Furthermore, not every intergranular crack will grow and propagate to the outer surface, or lead to a fatigue crack.

Our focus is to ensure we have done everything we can to prevent this type of material failure from happening again, as well as increase the likelihood of earlier detection of defects which can lead to this type of failure. Our ongoing efforts include a complete review of the blade and propeller assembly overhaul processes, developing new inspection techniques at the depot and field level, and researching new technologies to enable earlier detection of potential issues in the field. In this and every case, the Air Force review process seeks to identify root causes to mitigate and prevent future mishaps. Our goal is to provide the warfighter with the safest, mission-ready systems possible.

Since the mishap, the Warner Robins Air Logistics Complex and partners across the Air Force have worked with Navy and Marine officials to identify potential causes and to mitigate the risk of future mishaps. Our ongoing efforts include a complete review of the blade and propeller assembly overhaul processes, developing new inspection techniques at the depot and field level, and researching new technologies to enable earlier detection of potential issues in the field.

Due to the nature of the incident and the unknown factors at the time, the Independent Review Team recommended all blade overhaul work at Warner Robins Air Logistics Complex be halted pending a full review of the process. The IRT analyzed the production process and separated the inspection and overhaul process into 21 major steps to be completely reviewed before resuming C-130 propeller overhaul and assembly. The IRT decided to review each of the 21 steps along the following 9 categories: technical solutions; sufficiency of technical data; review of work control documents; the sequence of process operations; facilities; equipment; personnel training; personnel certification; and a full IRT review of each step.

We won’t be satisfied until we are confident we have the new process and technology in place to find corrosion and cracking earlier.

Q2. What could have been done differently?
A2. We are taking action both at field level and depot level to ensure we have done everything we can to prevent this type of material failure from happening again, as well as increasing the likelihood of earlier detection of defects which can lead to this type of material failure. Maintenance records are not available from 2011 and the investigation teams were not able to determine what specific actions were or were not taken for the propeller components involved in the mishap, therefore it’s hard to say what we could have done different.
Moving forward we are confident that the Independent Review Team is doing everything in their power to ensure we understand what happened from a physical/mechanical side in order to mitigate the risk of this happening again.

Q3. While propeller overhaul is still halted, how does this impact Robins?
A3. Currently WR-ALC is producing propeller assemblies with new (versus overhauled) blades while we continue to review the blade and propeller assembly overhaul processes, develop new inspection techniques at the depot and field level, and research new technologies to enable earlier detection of potential issues in the field. Propeller overhaul is a single product among thousands of components and multiple types of aircraft that are maintained and repaired at WR-ALC. Work continues on other commodities while we re-engineer our propeller inspection and overhaul processes.

Q4. Reports say there wasn’t quality control checks on every blade, why is that?
A4. Quality materials, equipment, processes, and training all impact safety. This is why the Air Force, Navy, Marine Corps and other industry partners are diligently working together on this issue. There is no question that this mishap revealed a need to re-examine all aspects of our lifecycle sustainment for these C-130 propeller blades. The prescribed process for blade inspection and overhaul dictates numerous quality control measures. Maintenance records are not available from 2011 and the investigation teams were not able to determine what specific actions were or were not taken for the propeller components involved in the mishap.

Q5. How is maintenance being done differently now?
A5. Since the mishap, the Warner Robins Air Logistics Complex and partners across the Air Force have worked with Navy and Marine officials to identify potential causes and to mitigate the risk of future mishaps. Our ongoing efforts include a complete review of the blade and propeller assembly overhaul processes, developing new inspection techniques at the depot and field level, and researching new technologies to enable earlier detection of potential issues in the field. One focus area is maximizing commonality of inspection and overhaul requirements for USAF and USN operations supporting the C-130 propeller system. When propeller overhaul production resumes at WR-ALC, the process will be largely similar for both USAF and USN propeller blades. There will remain a very small number of differences due to Service-unique propeller configurations and differing engineering assessments.

Q6. Was anyone in trouble for the incident?
A6. In accordance with Air Force policy at the time, depot-level work records were only maintained on file for two years, therefore maintenance records from 2011 are not available. As a result, we do not know who performed the maintenance on the mishap blade nor details on what maintenance was actually performed for this blade during the overhaul in 2011. In the short term all propeller overhaul records are being stored beyond the two year requirement, and in the long term the WR-ALC is looking into the use of electronic Work Control Documents that will be more easily archived and accessed. We are committed to a culture of accountability, quality, engaged supervision, and third-party verification of our compliance with technical and engineering guidance, written regulations and prescriptive publications, and safe industrial practices.

Q7. When an incident like this happens, what kind of toll is it on the morale of the base and among other Airmen?
A7. The workforce at WR-ALC is patriotic, conscientious, and quality-focused. They are extremely saddened by this mishap, as they are by any mishap involving our military and the weapon systems that they maintain, but are determined to prevent any occurrences like this from happening in the future.